[SPARK-8810] [SQL] Added several UDF unit tests for Spark SQL

One test for each of the GROUP BY, WHERE and HAVING clauses, and one that combines all three with an additional UDF in the SELECT.

(Since this is my first attempt at contributing to SPARK, meta-level guidance on anything I've screwed up would be greatly appreciated, whether important or minor.)

Author: Spiro Michaylov <spiro@michaylov.com>

Closes #7207 from spirom/udf-test-branch and squashes the following commits:

6bbba9e [Spiro Michaylov] Responded to review comments on UDF unit tests
1a3c5ff [Spiro Michaylov] Added several UDF unit tests for Spark SQL

sql/core/src/test/scala/org/apache/spark/sql/UDFSuite.scala

@@ -82,6 +82,76 @@ class UDFSuite extends QueryTest {
     assert(ctx.sql("SELECT strLenScala('test', 1)").head().getInt(0) === 5)
   }
 
+  test("UDF in a WHERE") {
+    ctx.udf.register("oneArgFilter", (n: Int) => { n > 80 })
+
+    val df = ctx.sparkContext.parallelize(
+      (1 to 100).map(i => TestData(i, i.toString))).toDF()
+    df.registerTempTable("integerData")
+
+    val result =
+      ctx.sql("SELECT * FROM integerData WHERE oneArgFilter(key)")
+    assert(result.count() === 20)
+  }
+
+  test("UDF in a HAVING") {
+    ctx.udf.register("havingFilter", (n: Long) => { n > 5 })
+
+    val df = Seq(("red", 1), ("red", 2), ("blue", 10),
+      ("green", 100), ("green", 200)).toDF("g", "v")
+    df.registerTempTable("groupData")
+
+    val result =
+      ctx.sql(
+        """
+         | SELECT g, SUM(v) as s
+         | FROM groupData
+         | GROUP BY g
+         | HAVING havingFilter(s)
+        """.stripMargin)
+
+    assert(result.count() === 2)
+  }
+
+  test("UDF in a GROUP BY") {
+    ctx.udf.register("groupFunction", (n: Int) => { n > 10 })
+
+    val df = Seq(("red", 1), ("red", 2), ("blue", 10),
+      ("green", 100), ("green", 200)).toDF("g", "v")
+    df.registerTempTable("groupData")
+
+    val result =
+      ctx.sql(
+        """
+         | SELECT SUM(v)
+         | FROM groupData
+         | GROUP BY groupFunction(v)
+        """.stripMargin)
+    assert(result.count() === 2)
+  }
+
+  test("UDFs everywhere") {
+    ctx.udf.register("groupFunction", (n: Int) => { n > 10 })
+    ctx.udf.register("havingFilter", (n: Long) => { n > 2000 })
+    ctx.udf.register("whereFilter", (n: Int) => { n < 150 })
+    ctx.udf.register("timesHundred", (n: Long) => { n * 100 })
+
+    val df = Seq(("red", 1), ("red", 2), ("blue", 10),
+      ("green", 100), ("green", 200)).toDF("g", "v")
+    df.registerTempTable("groupData")
+
+    val result =
+      ctx.sql(
+        """
+         | SELECT timesHundred(SUM(v)) as v100
+         | FROM groupData
+         | WHERE whereFilter(v)
+         | GROUP BY groupFunction(v)
+         | HAVING havingFilter(v100)
+        """.stripMargin)
+    assert(result.count() === 1)
+  }
+
   test("struct UDF") {
     ctx.udf.register("returnStruct", (f1: String, f2: String) => FunctionResult(f1, f2))